linux-kernel - Re: [PATCH] writeback: fix hung

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Message-ID: <20120613013018.GA5432@kernel>
Date:	Wed, 13 Jun 2012 09:30:19 +0800
From:	Wanpeng Li <liwp.linux@...il.com>
To:	Fengguang Wu <fengguang.wu@...el.com>
Cc:	Alexander Viro <viro@...iv.linux.org.uk>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	Gavin Shan <shangw@...ux.vnet.ibm.com>,
	Wanpeng Li <liwp.linux@...il.com>
Subject: Re: [PATCH] writeback: fix hung_task alarm when sync block

On Wed, Jun 13, 2012 at 09:18:17AM +0800, Fengguang Wu wrote:
>> >> @@ -1311,7 +1312,12 @@ void writeback_inodes_sb_nr(struct super_block *sb,
>> >>  
>> >>  	WARN_ON(!rwsem_is_locked(&sb->s_umount));
>> >>  	bdi_queue_work(sb->s_bdi, &work);
>> >> -	wait_for_completion(&done);
>> >> +	hangcheck = sysctl_hung_task_timeout_secs;
>> >> +	if (hangcheck)
>> >
>> >The hangcheck variable looks redundant.
>> 
>> if sysctl_hung_task_timeout_secs is equal to ZERO, it means 
>> timeout -- no checking done. So I think wait_for_completion_timeout 
>> makes no sense this time.
>
>I mean, you can test sysctl_hung_task_timeout_secs directly?
>It's a one shot test anyway.

/*
 * Zero means infinite timeout - no checking done:
 */
unsigned long __read_mostly sysctl_hung_task_timeout_secs = CONFIG_DEFAULT_HUNG_TASK_TIMEOUT;

The comment in kernel/hung_task.c says "Zero means infinite timeout - no
cheking done". Maybe I can just test if this time alarm doesn't flood my
logs. Do you have more suggestion. :-)

Regards,
Wanpeng Li

>
>> >> +		while (!wait_for_completion_timeout(&done, HZ/2))
>> >> +			;
>> >> +	else
>> >> +		wait_for_completion(&done);
>> >>  }
>> >>  EXPORT_SYMBOL(writeback_inodes_sb_nr);
>> >>  
>> >> -- 
>> >> 1.7.9.5
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